Optical fiber connectors and splicing devices are an important part of substantially any optical fiber communication system. For instance, connectors or splicing devices may be used to join segments of fiber into longer lengths or to connect fiber to active devices such as radiation sources, detectors, or repeaters, or to passive devices such as switches or attenuators. Considering that a core of multimode optical fiber is 50 microns in diameter and that of single mode fiber is only 8 microns, achieving a proper connection or splice is no small task. Due to the precision required to adequately join two optical fibers and the importance of such splices not introducing an unacceptable amount of loss into the communication system, verification of a proper connection would be beneficial.
A multimode fiber splicing technique presently exists which uses precision glass plugs to terminate fibers and a plastic ferrule to align and retain the plugs. A completed splice assembly of this technique assures its mechanical integrity by means of axial loading applied with coiled springs at the plug ends. In addition, the splice assembly is index matched with a curable gel. More specific details of such a splice are disclosed in commonly assigned U.S. Pat. No. 4,880,291 issued in the names of J. A. Aberson, G. F. DeVeau and K. M. Yasinski.
In the above-described connector or splice, a loss minima may be obtained by rotating plugs relative to each other. Some of the factors affecting the particular loss minima include 1) eccentricities caused by the position of the fiber core within the cladding; 2) the position of the fiber within the plug bore, and 3) the position of the bore relative to the plug outer diameter.
Two methods presently used to monitor splice loss during plug rotation are end-to-end transmission measurements and Optical Time Domain Reflectometer (OTDR) measurements. Using end-to-end transmission measurements to obtain a minimum splice loss requires that a source (light-emitting diode or laser) be used to energize the fiber to be spliced and that a suitable detector and power-measuring apparatus be located at the far end of the fiber to be spliced. For field splicing this would usually require a source in the central office and the detector (typically a power meter) at the splice point adjacent to the splice being made. Basic shortcomings with this method of splice optimization are the necessity of opening the adjacent manhole with two splicing teams required, the inability to accurately measure splice loss due to the fiber losses included in the measurement, and difficulties involving feeding back the transmitted power level to the splicer.
The OTDR method of splice alignment requires connection to the fiber to be spliced and a talk circuit between the OTDR and splicing crew. As the splice is aligned, the splice loss from the OTDR is reported to the splicer. This procedure of measuring and adjusting is repeated until the splice is optimized. Splice loss measured with unidirectional OTDR measurements is inaccurate due to fiber parameter differences. Accurate OTDR splice loss measurements require measurements from both directions and averaging. An additional disadvantage of OTDR is the associated low sampling rate. Yet another disadvantage of the OTDR is its range. With state-of-the-art equipment, only a relatively limited range may be allowed before the OTDR must be moved closer to the splice point.
In light of the above-identified problems with the present splice verifying technology, what is needed and what is seemingly not provided by the prior art is a dependable system capable of providing splice optimization and loss measurement at the splice point. The sought-after system should be usable to adjust or "tune" an optical fiber splice for minimum loss and continually indicate the amount of loss in decibels.